The present invention relates to an image display and a method of manufacturing the same, and particularly to a technology effective for application to a display apparatus which has thin-film electron emitters having an electrode-insulator-electrode structure to emit electrons into vacuum.
The thin-film electron emitters are electron-emitter elements each using hot electrons produced by applying a high electric field to an insulator.
As a typical example, an MIM (Metal-Insulator-Metal) electron emitter comprising a thin film having a three-layer structure of a top electrode-insulating layer-base electrode will be explained.
FIG. 14 is a diagram for describing the principle of operation of an MIM electron emitter illustrated as a typical example of a thin-film electron emitter.
A driving voltage is applied between a top electrode 11 and a base electrode 13 to set an electric field within a tunneling insulator 12 to 1 MV/cm to 10MV/cm and over. Thus, electrons placed in the neighborhood of the Fermi level in the base electrode 13 are transmitted through a barrier by tunneling phenomena. Thereafter, they are injected into the conduction bands of the tunneling insulator 12 and top electrode 11, thereby resulting in hot electrons.
Some of these hot electrons are subjected to scattering under interaction with a solid in the tunneling insulator 12 and the top electrode 11, thus leading to the loss of energy.
As a result, hot electrons having various energies exist when they have reached an interface between the top electrode 11 and vacuum 10.
Of these hot electrons, ones having energy larger than the work function xcfx86 of the top electrode 11 are emitted into the vacuum 10, and ones other than the above ones flow into the top electrode 11.
Assuming that a current based on the electrons flowing from the base electrode 13 to the top electrode 11, is called a diode current (Id), and a current based on the electrons emitted into the vacuum 10 is called an emission current (Ie), an electron emission efficiency (Ie/Id) ranges from about 1/103 to about 1/105.
Incidentally, the MIM thin-film electron emitter has been described in, for example, Japanese Patent Application Laid-Open No. Hei 9-320456.
Now, the top electrode 11 and the base electrode 13 are provided in plural form and these plural top electrodes 11 and base electrodes 13 are formed orthogonal to one another to thereby form thin-film electron emitters in matrix form. Consequently, electron beams can be produced from arbitrary locations and hence they can be used as electron emitters for a display apparatus.
Namely, a display apparatus can be constructed wherein thin-film electron-emitter elements are placed at every pixel, and electrons emitted therefrom are accelerated in vacuo and thereafter applied to each of phosphors to thereby allow the applied phosphor to emit light, whereby a desired image is displayed thereon.
The thin-film electron emitters have excellent features as electron-emitter elements for the display apparatus in that they are capable of implementing a high-resolution display apparatus because the emitted electron beams are excellent in directionality, and they are easy to handle because they are insusceptible to the influence of their surface contamination, for example.
In the display apparatus using the conventional thin-film electron emitters, when one of a large number of thin-film electron-emitter elements (electron emission regions) placed in matrix form was short-circuited due to a failure in manufacture thereof or other reasons, no electrons were emitted from all the thin-film electron-emitter elements on a row or/and a column to which such a thin-film electron-emitter element was connected, thus causing no light emission. Namely, a xe2x80x9cpoint defectxe2x80x9d of one thin-film electron-emitter element has caused a xe2x80x9cline defectxe2x80x9d.
The above-described point will be explained below.
FIG. 15 is a diagram showing a schematic configuration of a conventional thin-film electron-emitter matrix.
Thin-film electron-emitter elements 301 are respectively formed at points where row electrodes (base electrodes) 310 and column electrodes (top electrodes) 311 intersect respectively.
Incidentally, while the thin-film electron-emitter matrix is illustrated with 3 rows and 3 columns in FIG. 15, the thin-film electron-emitter elements 301 are actually placed by the number of pixels constituting a display apparatus, or the number of sub-pixels in the case of a color display apparatus.
Now, the respective thin-film electron-emitter elements 301 are directly connected to the row electrodes 310 and the column electrodes 311 respectively.
Therefore, when, for example, a thin-film electron-emitter element 301 placed at an intersection (R2, C2) of a row electrode 310 of R2 and a column electrode 311 of C2 is short-circuited due to a failure in manufacture thereof or the like, the row electrode 310 of R2 and the column electrode 311 of C2 are short-circuited. Hence even if an attempt were made to apply a suitable voltage to both electrodes from a row electrode driving circuit 41 or a column electrode driving circuit 42, the voltage would not be applied thereto.
Therefore, all the thin-film electron-emitter elements 301 on the row electrode of R2, or/and all the thin-film electron-emitter elements 301 on the column electrode 311 of C2 are not operated, thus causing a xe2x80x9cline defectxe2x80x9d.
Even if elements equivalent to about {fraction (1/10000)} of the total number of pixels have xe2x80x9cpoint defectsxe2x80x9d in a matrix-type display apparatus such as a liquid-crystal display apparatus or the like, no problem occurs from a practical standpoint and they can be used in most cases.
Namely, about 100 xe2x80x9cpoint defectsxe2x80x9d can be allowed in the case of a display apparatus configured in 480xc3x97640xc3x973 dots, for example.
However, one having a xe2x80x9cline defectxe2x80x9d such as non-light emission of all elements on one line cannot be used as a display apparatus.
Thus, the display apparatus using the conventional thin-film electron emitters was accompanied by a problem that the xe2x80x9cpoint defectsxe2x80x9dproduced the xe2x80x9cline defectxe2x80x9d, thereby reducing production yields.
The present invention has been made to solve the problem of the prior art. An object of the present invention is to provide a technology capable of enhancing production yields in an image display.
The above, other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
Summaries of typical one of the inventions disclosed in the present application will be described in brief as follows:
There is provided an image display which comprises a display device including a first plate which has a plurality of electron-emitter elements each having a structure comprised of a base electrode, an insulating layer and a top electrode stacked on one another in this order, the electron-emitter element emitting electrons from the surface of the top electrode when a voltage of positive polarity is applied to the top electrode; a plurality of first electrodes for respectively applying driving voltages to the base electrodes of the electron-emitter elements lying in a row (or column) direction, of the plurality of electron-emitter elements; and a plurality of second electrodes for respectively applying driving voltages to the top electrodes of the electron-emitter elements lying in the column (or row) direction, of the plurality of electron-emitter elements, a frame component, and a second plate having phosphors, whereby a space surrounded by the first plate, the frame component and the second plate is brought to vacuum, wherein at least one the electron-emitter element includes its corresponding base electrode and top electrode at least one of which is connected to the first electrode or second electrode through a resistor element.
Namely, the present invention is characterized in that a resistor is inserted between a column electrode and a thin-film electron-emitter element or between a row electrode and a thin-film electron-emitter element, or resistors are respectively inserted between a column electrode and a thin-film electron-emitter element and between a row electrode and a thin-film electron-emitter element.
FIG. 1 is a diagram showing a schematic configuration of one example of a thin-film electron-emitter matrix of an image display of the present invention.
The image display shown in FIG. 1 is equipped with a thin-film electron-emitter matrix in which resistors 305 are respectively inserted between column electrodes 311 and thin-film electron-emitter elements 301.
Incidentally, the resistors 305 will be called pixel resistors in the following description.
While one pixel is formed of a combination of respective sub-pixels of red, blue and green in the case of a color image display, the xe2x80x9cpixelsxe2x80x9d defined herein are equivalent to the sub-pixels in the case of the color image display. In the present specification, pixels in the case of a monochrome image display, and sub-pixels in the case of a color image display are also called xe2x80x9cdotsxe2x80x9d.
Consider where the resistance value of the resistor 305 is set to 10 times or more the output impedance of each column electrode driving circuit 42. Since the resistance between a row electrode 310 of R2 and a column electrode of C2 is sufficiently larger than the output impedance of the corresponding driving circuit even if a thin-film electron-emitter element 301 at (R2, C2) is short-circuited, a sufficient voltage is applied to both electrodes and hence other thin-film electron-emitter elements 301 on both electrodes normally operate. Of course, the thin-film electron-emitter element 301 at (R2, C2) does not operate.
Thus, the present invention is capable of preventing the xe2x80x9cpoint defectsxe2x80x9d from leading to the xe2x80x9cline defectxe2x80x9d.
The following restrictions are imposed on the resistance value (Rr) of the pixel resistor 305.
Assuming that capacitance obtained by adding together parasitic capacitance of each thin-film electron-emitter element per se and parasitic capacitance within one pixel is defined as Ce, Cexc2x7Rr results in time constant of a change in signal voltage applied to the corresponding thin-film electron-emitter element 301.
Thus, (Cexc2x7Rr less than 1H) must be taken when used as the display apparatus.
Here, 1H indicates a horizontal scanning period. Assuming that a field frequency is defined as f and the effective number of scan lines is defined as Neff (when two lines are simultaneously driven: (the number of scan lines÷2)), the horizontal scanning period (1H) is given by the following equation (1):
xe2x80x831H=1/(fxc2x7Neff)xe2x80x83xe2x80x83(1)
When f=60 Hz and Neff=256, for example, 1H=64 xcexcs is obtained.
A second effect of the present invention resides in that the influence of deviations in characteristics of wire resistance and a driving circuit can be reduced.
Such a functional relation as expressed by the following equation (2) is established between a diode voltage (Vd) applied between both electrodes (top electrode 11 and base electrode 13) of the thin-film electron emitter 301 and a diode current (Id) flowing therebetween:
Id=f(Vd)xe2x80x83xe2x80x83(2)
On the other hand, the total wire resistance of the row electrodes 310 and column electrodes 311 is defined as R(line) the output impedance of each row electrode driving circuit 41 is defined as Zout(row), and the output impedance of each column electrode driving circuit 42 is defined as Zout(column).
Assuming that the difference between a voltage outputted from the row electrode driving circuit 41 and a voltage outputted from the column electrode driving circuit 42, i.e., an externally applied voltage is defined as V0, the diode voltage (Vd) applied across the thin-film electron-emitter element 301 is expressed in the following equation (3):
Vd=V0xe2x88x92Id(R(line)+Zout(row)+Zout(column))xe2x80x83xe2x80x83(3)
Thus, the diode current (Id) that flows through the thin-film electron-emitter element 301, is expressed in the following equation (4):
Id=f [V0xe2x88x92Id(R(line)+Zout(row)+Zout(column))]xe2x80x83xe2x80x83(4)
Therefore, when deviations xcex94R(line), xcex94Zout(row) and xcex94Zout(column) exist in R(line), xcex94Zout(row) and xcex94Zout(column), respectively, the diode current (Id) also varies in its current value.
A current (emission current) (Ie) emitted into vacuum from the thin-film electron-emitter element 301 varies according to the current value of the diode current (Id).
Accordingly, brightness non-uniformity occurs in the display apparatus.
In the present invention, the resistors 305 are inserted every thin-film electron-emitter elements. Assuming that the resistance value of the resistor 305 is defined as Rr, a diode voltage (Vd) applied across the thin-film electron-emitter element 301 is expressed in the following equation (5):
Vd=V0xe2x88x92Id(Rr+R(line)+Zout(row)+Zout(column))xe2x80x83xe2x80x83(5)
Then, Rr is set so as to become larger than the deviations xcex94R(line), xcex94Zout(row) and xcex94Zout(column). Consequently, these deviations will not cause a deviation in the current value of the diode current (Id) and hence no brightness non-uniformity occurs.
Next consider the influence of a deviation in the resistance value of the pixel resistor 305 on a deviation in the amount of the emission current.
Let""s assume that the externally applied voltage V0 is applied over all. The influence of the deviation in the resistance value R of the pixel resistor 305 on the current that flows through the thin-film electron-emitter element 301 is estimated.
Assuming that the diode current-voltage characteristics of the thin-film electron-emitter element 301 are represented as Id=f(V), and currents that flow when the resistance value of the pixel resistor 305 is given as R and R+xcex94R, are respectively defined as I and I+xcex94I, the relation expressed in the following equation (6) is established:                                                         Δ              ⁢                              xe2x80x83                            ⁢              I                        I                    =                                    (                                                Δ                  ⁢                                      xe2x80x83                                    ⁢                  R                                                  R                  +                                      Δ                    ⁢                                          xe2x80x83                                        ⁢                    R                                                              )                        /                          (                              1                +                α                            )                                      ⁢                  
                ⁢                  α          =                                    r              e                                      R              +                              Δ                ⁢                                  xe2x80x83                                ⁢                R                                                    ⁢                  
                ⁢                              r            e                    =                                    ⅆ              V                                      ⅆ                              I                d                                                                        (        6        )            
Thus, if the resistance value R+xcex94R of the pixel resistor 305 is set smaller than a differential resistance re of the thin-film electron-emitter element 301 (in an operation region).
If xcex1xe2x89xa71 is established, then the above equation (6) can be transformed as the following equation (7):                                           Δ            ⁢                          xe2x80x83                        ⁢            I                    I                ≤                              1            2                    ⁢                      (                                          Δ                ⁢                                  xe2x80x83                                ⁢                R                                            R                +                                  Δ                  ⁢                                      xe2x80x83                                    ⁢                  R                                                      )                                              (        7        )            
Thus, the influence of the deviation xcex1R in the resistance value of the pixel resistor 305 on uniformity of a displayed image is lessened.
In other words, the allowance of the deviation in the resistance value of the pixel resistor 305 becomes large and hence the display apparatus is easy to be manufactured.
The present invention provides a display apparatus which comprises a display device including a first plate which has a plurality of electron-emitter elements each having a structure comprised of a base electrode, an insulating layer and a top electrode stacked on one another in this order, the electron-emitter element emitting electrons from the surface of the top electrode when a voltage of positive polarity is applied to the top electrode; a plurality of first electrodes for respectively applying driving voltages to the base electrodes of the electron-emitter elements lying in a row (or column) direction, of the plurality of electron-emitter elements; and a plurality of second electrodes for respectively applying driving voltages to the top electrodes of the electron-emitter elements lying in the column (or row) direction, of the plurality of electron-emitter elements, a frame component, and a second plate having phosphors, whereby a space surrounded by the first plate, the frame component and the second plate is brought into vacuum, wherein the at least one electron-emitter element includes its corresponding base electrode and top electrode at least one of which is connected to the first electrode or second electrode through a resistor element or a connection wire.
In the present invention, when a defect due to a short circuit of the thin-film electron-emitter element 301 is found at a production stage, the corresponding element is cut off to thereby enable prevention of the occurrence of the xe2x80x9cline defectxe2x80x9d.
FIG. 16 is a plan view showing a thin-film electron-emitter element structure of a conventional thin-film electron-emitter matrix.
In the conventional thin-film electron-emitter matrix as shown in FIG. 16, thin-film electron-emitter elements 301 are respectively formed at regions where row electrodes 310 and column electrodes 311 spatially overlap in fact. It was therefore difficult to separate only the thin-film electron-emitter elements 301 from the row electrodes 310 or column electrodes 311.
In the present invention, as will be described in detail in the following embodiments, electron-emitter structures of respective pixels are devised to thereby easily separate thin-film electron-emitter elements 301 at specific pixels through the use of a laser repair technology or breakage by current-heating, whereby the occurrence of xe2x80x9cline defectsxe2x80x9d can be lessened.
Incidentally, a prior-art search has been carried out based on the result of the present invention from the viewpoint that the resistors are formed in every pixels.
As a result, the corresponding art has not been found in the display apparatus using the thin-film electron emitters, which is intended for the present invention.
As a result of a further investigation of objects to be researched, which is extended up too other-types electron emitters, an example in which a resistive sheet is inserted into individual pixels in field-emission electron emitters, has been found out in EURODISPLAY"" 90, 10th International Display Research Conference Proceedings (vde-verlag, Berlin, 1990), pp. 374-377.
This reference describes a field-emitter array comprising multiplicity of electron-emitting tips(emitter tips) for each pixel. By introducing a resister sheet which functions as resistance independently for each emitter tip, a negative feedback resulting from the voltage drop in the resistor at each emitter tip averages the current deviation among the every emitter tips in each pixel, and thereby alleviating the deviation.
The reference above mentioned aims to solve the problem that only specific emitter tips inside a pixel emit a large current, thus generating xe2x80x9cbright spotsxe2x80x9d inside the pixel which causes degradation in image quality.
Further, the technology described in the known art encounters difficulties in cutting off a defect pixel with laser beam irradiation or the like for defect repairing.